Various devices for respiratory assistance are known, such as oral, nasal, endotracheal and tracheotomy probes and cannulas, which are designed to form the junction between an artificial respiration and/or anesthesia apparatus and the respiratory system of a patient.
Depending on the circumstances, these devices comprise a tube which forms a main channel designed to be connected, via its distal end, to an airway of a patient such that this main channel connects the respiratory system of the patient to the outside, the device often comprising at least one auxiliary channel which, for example, is formed in the wall of said tube and is connected to a source of respiratory gas, so as to permit the injection of a constant or pulsed jet of respiratory gas (oxygen, air or a mixture of air and oxygen) intended to ventilate the patient, this auxiliary channel opening into the main channel in the vicinity of the distal end of the latter.
It is also known that, when using such a device on a patient in cardiac arrest, the restarting of the heart by cardiac massage can be detected by measuring the partial pressure of carbon dioxide EtCO2 (end-tidal CO2) in the vitiated air exhaled by the patient by means of an analyzer, for example a capnometer. EtCO2 is a parameter that is dependent on two important vital functions of the body, namely ventilation and blood flow, such that it provides a simple reflection of the efficacy of the cardiac massage. Thus, it is known to analyze the vitiated air exhaled by the patient at the outlet of the proximal end of the respiratory assistance device in such a way as to determine the presence of EtCO2 and thereby detect a possible restart of the patient's heart.
However, the vitiated air emerging from such a respiratory device is generally diluted by respiratory gas introduced into the main channel by way of the auxiliary channel(s). It then often happens that the small quantity of EtCO2 present in the vitiated air, and representative of the onset of the restart of the heart, is so diluted that it is not detected by the capnometer. Therefore, the operators manipulating the device for artificial respiration are alerted to the restart of the heart only when the quantity of EtCO2 in the diluted vitiated gas exceeds a certain detection threshold (the heart by then having already been restarted for some moments). They therefore continue to perform the cardiac massage, which involves alternate compression and decompression exerted on the thoracic cage of the patient, at least until they are informed of the restart of the heart.
However, if this cardiac massage is performed over a prolonged period, it frequently produces, in the patient's lungs, lesions that may cause bleeding.
It is therefore preferable if the restart of the heart is indicated as soon as possible to the operators, such that they stop massaging the thoracic cage of the patient as early as possible and provide other and more appropriate care.